Electroluminescent matrix and access device



1963 A. M. WITTENBERG ELECTROLUMINES CENT MATRIX AND ACCESS DEVICE FiledApril 21, 1960 3 Sheets-Sheet 1 ELECTROLUM/NESCENT ELEMENTPHOTOCONDUCT/VE ELEMENT INVENTOR A. M W/TTENBERG ATTORNEK Fe 9, 1963 A.M. WITTENBERG ELECTROLUMINESCENT MATRIX AND ACCESS DEVICE Filed April21. 1960 5 Sheets-Sheet 2 F/GZA LAYER TRANSPARENT CONDUCT/V5 LAYERELECTROLUM/NESCENT CONDUCTIVE nacmoos FIG. 2B

R mm 0 A R L 05 MW MW W W40 w m nu C m 0 Wm M N C 0 0 E C H T v. P mu mw m m INVENTOR A. M. W/fTENBE/PG ATTORNEV Feb. 19, 1963 A. M. WITTENBERGI ELECTROLUMINESCENT MATRIX AND ACCESS DEVICE Filed April 21. 1960.

3 Sheets-Sheet 3 INVE/VTOR AM. W/TZENBERG By l I I l l I l l ATTORNEYUnited States Patent 3,078,373 ELECTROLUMINESCENT MATRIX AND ACCESSDEVICE Albert M. Wittenherg, Orange, N.J., assignor to Bell TelephoneLaboratories, Incorporated, New York,

N.Y., a corporation of New York Filed Apr. 21, 1960, Ser. No. 23,820 19Claims. (ill. 250-213) This invention relates to electroluminescentdevices and, more particularly, to electroluminescent matrix and accessunit combinations.

Electroluminescent matrix devices as known in the art generally comprisesmall electroluminescent electrodes sandwiched between a large number ofthin column and row conducting elements. Normally, one end of eachconductor is exposed and equipped with a set of terminals. The terminalsare often in the form of contacting surfaces serving as wiper contacts,or they may be connected by wiring to terminals of a wiper switch,electrical shift register, or other such activating means, thus forminga matrix-access unit combination.

Establishing the terminal connections mentioned above presents a majorproblem in that the column and row conductors of this type of matrix arenot amenable to standard techniques for forming electrical connections.The above problem exists because the conductors generally comprise anextremely thin coating of a metal which is vacuum plated on a surface ina pattern of parallel conductors spaced a short distance apart, or ispainted on the surface as thin, narrow strips. Regardless of the methodused in forming the conductive coating, it is extremely diflicult toattach satisfactory electrical connections to such thin and fragileconductive coatings. Furthermore, the connection problem is magnified inthat it is necessary to further attach the electrical connections madeto the matrix conductors to distinct individual activating units. Thisprocedure makes such devices fragile, unwieldly, and thus unattractivefor a wide variety of applications.

Accordingly, it is a general object of my invention to provide animproved electroluminescent device. More specifically, it is an objectof this invention to provide an improved electroluminescentmatrix-access unit combination.

It is a further object of my invention to provide a simple, ruggedmatrix-access combination.

It is another object of my invention to provide a compact, unitaryelectroluminescent matrix-access circuit.

These and other objects of my invention are attained in one illustrativeembodiment wherein the access circuitry for an electroluminescent matrixcomprises radiation-generating and radiation-responsive elements whichproduce a spot of light that moves along a predetermined path at acontrolled rate; The light thus emitted from the access circuitryimpinges a second set of radiation-responsive elements electricallyconnected in the matrix. The second group elements in turn act asindividual switches to allow the application of an activating potentialto selected portions of the matrix device so as to produce controlledspots of luminescence.

The access circuitry has a plurality of stages arranged in distinctcoordinates with respect to the matrix, each stage of which includes aparallel combination of a radiation-responsive and radiation-generatingelement that is connected in a series circuit with anotherradiationresponsive element. Voltages are established across the stagesof the coordinate devices in such a manner that a radiation-generatingelement of a selected stage is activated. The selection is accomplishedby directing a por- 3,078,373 l Patented Feb. 19, 1963 tion of the lightemitted from the activated element in one stage to a light-responsiveelement in a succeeding stage, priming that stage so that a subsequentincrease in the applied voltage activates a radiation-generating elementtherein. The element so activated supplies radiation to the prior stageto cause termination of the activated element therein. By this selectiveestablishment of voltages across the various stages, moving spots oflight are developed along the coordinate access units.

These coordinate access units are situated in a light transferrelationship with a second group of radiationresponsive elements locatedin the matrix. Each of this second group of elements acts as a switch ina distinct one of a plurality of column and row conductors, whichconductors are positioned on opposite sides of an electroluminescentmaterial to form an electroluminescent matrix as known in the art. Themoving spots of light shining on the radiation-responsive elements ofthe matrix activates those elements so as to complete a path between anactivating potential source and selected portions of theelectroluminescent material, thereby causing such selected portions toluminesce.

I have found then that the use of radiation-responsive elements actingas switches between an activating potential source and the column androw conductors of an electroluminescent matrix provide a compact meansof gaining access to the matrix crosspoints when utilized in combinationwith coordinate access circuits radiating light from preselectedlight-generating elements. As all of the requisite component elementsare amenable to known vacuum coating techniques, the entire unit may bedisposed on a suitable transparent supporting member, thus eliminatingany distinct electrical connections between the matrix and thecoordinate access units.

Accordingly, it is a feature of my invention that an electroluminescentmatrix is electrically isolated from the coordinate access units, thematrix activations being derived from input illumination signals emittedfrom distinct electroluminescent elements.

It is another feature of this invention that the requisitematrix-activating illumination is delivered from distinct coordinateaccess units having a plurality of stages, each stage of which iscomprised of an electroluminescentphotoconductor parallel combination ina series circuit with another photoconductive element.

It is a further feature of my invention that the access stages and thecoordinate matrix are all mounted on a common transparent plate. Morespecifically in accordance with this feature of my invention aconductive electrode on each electroluminescent element in an accessstage is positioned to reflect the light from its electroluminescentelement back through the common transparent mounting plate to fourphotoconductive elements, namely the photoconductive element in serieswith this electroluminescent element in the access circuitry, thephotoconductive element in series with the electroluminescent element inthe next stage in the access circuitry, the photoconductive element inparallel with the electroluminescent element in the prior stage in theaccess circuitry, and the photoconductive element in series with thecoordinate lead of the matrix for that stage.

A complete understanding of these and other features of this inventionmay be gained from consideration of the following detailed descriptiontogether with the accompanying drawing in which:

FIG. 1 is a schematic arrangement partially in block diagram form of anelectroluminescent matrix and access unit combination illustrative ofone specific embodiment of my invention;

FIGS. 2A and 2B are exploded views of the constructional details of asection of a coordinate access unit which may be utilized in theembodiment of FIG. 1,

FIG. 3 illustrates the constructional details of the coordinate accessunit section and one crosspoint portion of the matrix; and

FIG. 4, 5, and 6 illustrate three views of the constructionalarrangement of a portion of the matrix-access unit combination shownschematically in FIG. 1.

Turning now to FIG. 1, the combination is shown comprising theelectroluminescent matrix 1i) and row and column coordinate access units40 and 40', respectively. Access unit 40, shown in FIG. 1, is composedof a series of stages utilizing radiation-responsive andradiation-generating elements. For purposes of illustration, only fourstages are shown, though any desired number might advantageously beutilized. Each stage consists of a radiation-responsive orphotoconductive element in series with a parallel combination of anotherphotoconductive element and a radiation-generating or electroluminescentelement.

As is well known in the art, the electroluminescent elements, which maybe made of a material such as zinc sulfide phosphor, are a means forgenerating visible or near visible radiation. The photoconductiveelements, which as well known in the art may be made of a material suchas cadmium sulfide crystal, are responsive to radiation emitted from theelectroluminescent elements to reduce the photoconductors normally highimpedance.

The circuit operation of row coordinate access unit 40 may best beexplained by assuming that switch 44 is in the closed position, therebyconnecting potential source 52 in parallel across the various stages ofthe access unit 40. Source 48, it is to be understood, is a highimpedance generator so chosen as not to be adversely affected by theshunt placed across it by the closure of switch 44. Potential source 52establishes a voltage which alone is insuflicient in magnitude toactivate any one of the electroluminescent elements 42, 46, 50, or 54 sothat no operation is taking place at this time.

When the activation of the row coordinate access unit 40 is desired, asmall amount of li ht is briefly applied to photoconductive element 41from external source 56, which source may advantageously be a light, anelectroluminescent element, or other radiation-generating means. It iswell known in the art that in the presence of radiation of a certainwave length and intensity to which it is responsive, a photoconductorprovides a low impedance to current flow, and conversely, in the absenceof such radiation, is photoconductor provides a high impedance tocurrent flow. Assuming that radiation of the proper intensity and wavelength is emitted by source 56 and shines, via light channel 57 onphotoconductive element 41, that elements impedance will be reduced to alow level. This operation will establish a voltage from source 52 acrosselectroluminescent element 42, thereby causing it to glow dimly. Theelectroluminescent element 42 supplies radiation, in turn, tophotoconductive elements 41 and 45 via light channels 58 and 59,respectively. Electroluminescent element 42 also supplies radiation, vialight channel 70, to another photoconductor 13, the purpose of whichwill be explained in detail later. The above radiation delivered byelectroluminescent element 42, being only a minute amount, lowers theresistance of photoconductor 41 slightly; however, no further operationwould take place at this time without a higher voltage establishedacross the various stages of access unit 46.

The higher potential is developed at a desired instant by the momentaryopening of switch 44 which connects potential source 4-8 in series withpotential source 52, thereby increasing the voltage acrosselectroluminescent element 42 by an amount sufficient to cause thatelement to glow brightly. As mentioned, the radiation generated byelement 42 is fed by light channels 58 and 59 to photoconductiveelements 41 and 45. This feedback radiation via light channels 53 and 59is in a regenerative direction tending to drive the photoconductiveelements 41 and 45 into an even lower impedance condition. Owing to thenormal photoconductor impedance characteristics, a large change ofimpedance occurs when a relatively small change in radiation is directedto the photoconductive element. Thus element 42 is shining enough lighton the series associated photoconductive element 41 to maintain thatelements resistance at the low level required to permit sufiicientvoltage across electroluminescent element 42 to keep the latter elementglowing brightly. This feedback radiation is sufficient to maintain thephotoconductor-electroluminescent series combination 41, 42 in a stableon condition after the switch 44 is closed, thereby shunting potentialsource 48 and leaving only potential source 52 to deliver voltage to thefirst stage of access unit 40.

The operation as thus described will persist with the first stage in theon condition and the other stages in the OE condition until switch 44 isagain operated. However, prior to the operation of switch 44, the radiation delivered by element 42 via light channel 59" to photo-- conductor45 has allowed sufficient voltage from source 52 to be impressed acrosselectroluminescent element 46 to cause that element to glow dimly. Atthe desiredinstant, switch 44 may again be opened momentarily to impressa voltage from both potential sources 48 and 52 across the access unitstages. electroluminescent element 46 to glow brightly and de liverradiation via light channels 61, 62, 63 to photo-" conductive elements43, 45, and 49, respectively.

As photoconductive element 43 is in a shunt relation withelectroluminescent element 42, the radiation supplied via light channel61 reduces the impedance of photoconductive element 43. This impedancedrop reduces the voltage across photoconductive element 43 andelectroluminescent element 42 in succession, thus reducing theenergizing current through electroluminescent element 42. This reductionin energizing current results in a substantial decrease in the radiationgiven oil by that element. Thus a decrease in feedback radiation toseries photoconductor 41 results, and an increase in the impedance ofphotoconductor 41 is established which further decreases the radiationgiven off by electroluminescent element 42. This feedback actioncontinues until electroluminescent element 42 is fully extinguished.

As mentioned earlier, the electroluminescent element 42 suppliesradiation via light channel 59 to photoconductive element 45. Thetermination of luminescence in element 42 would, in turn, have increasedthe impedance of photoconductive element 45 were it not for theregenerative operation taking place between that element andelectroluminescent element 46. In other words, the photoconductiveelement 45 is placed in the saturated impedance condition by theradiation delivered via light channel 62 from electroluminescent element46;. thus the photoconductive element 45 remains essentially unaffectedby the absence of radiation in light channel 59 due to the terminationof luminescence in electrolumi-- nescent element 42.

The access unit 40 now has stage one in the oft condition and stage twoin the on condition. This condition will persist, of course, untilswitch 44 is once again momentarily opened so as to establish the OEcondition in the second stage and induce the on condition in the thirdstage. The above-described operation may then be repeated at desiredintervals merely by the selective operation of switch 44.

The other coordinate access unit 40' functions in the same mannerdiscussed above for unit 40 and is comprised of similar componentsdesignated by prime numbers.

The access units 40 and 40' are situated so as to be optically connectedto the electroluminescent matrix unit 10, which advantageously is of thetype known in the art utilizing painted or vacuum coated column and rowconductors that are separated by a contiguous layer or This high voltagecauses-- distinct electrodes of electroluminescent material. The matrixthus formed is represented schematically by the horizontal rows 11 andthe vertical columns 12. The electroluminescent layer, contiguous to andbetween the rows and columns 11 and 12, defines a plurality ofcross-points 28 through 39. The row and column conductors 11 and 12contain photoconductive elements 13, 15, 17, 19 and 14, 16, 18,respectively. A common potential source 25 is connected to the row andthe column conductors 11 and 12 by these photoconductive elements.

In the absence of radiation, these photoconductive elements would be intheir high impedance condition thus preventing the application ofpotential from source 25 across any portion of the electroluminescentmatrix 19. This condition would exist when both the row and columncoordinate access units are in the unactivated condition. The selectiveactivation of the row and column coordinate access units will producespots of light which will shine on particular ones of the matrixphotoconductive elements, reducing those elements impedance and thusallowing application of potential from source 25 to opposite sides ofthe electroluminescent layer.

It should be noted that the row and column coordinate access units 40and 41) would have to activate two particular photoconductive elementswhich define one distinct crosspoint before a voltage is impressed onboth sides of that electroluminescent element causing it to luminescebrightly. Consider for the purposes of illustration that the row accessunit 40 has the second stage in the on condition with, of course, theremaining ones in the off condition, while at the same instant, thecolumn acccess unit 40' has the first stage in the on condition and theremaining stages in the ofif condition. This situation provides aluminous state in elements 42' and 46 in units 4t! and 40, respectively.

The radiation emitted by electroluminescent element 46 will betransmitted via the light channel 71 to photoconductive element 15. Atthe same instant in the column access unit, the radiation emitted fromthe activated electroluminescent element 42 will be delivered via lightchannel 70' to photoconductive element 18. Photoconductive elements 15and 18 are designed such that the received radiation reduces theirnormally high impedance states to low impedance states. This reductionin impedance allows potential source to apply an activating voltage toboth sides of electroluminescent element 33, thereby causing thatelement to glow brightly.

Assume that in the next operation switch 44 was left in the opencondition and switch 44' was momentarily closed. Element 46 in the rowaccess unit would continue to luminesce, while in the column accessunit, element 42' would be extinguished and element 46 would luminescein the manner described above. This operation would leave rowphotoconductive element 15 in a low impedance state due to the radiationdelivered from electroluminescent element 46 via light channel 71.However, column photoconductive element 18 would now return to a highimpedance state due to the absence of radiation, since element 42 is inan unactivated condition. The activation of electroluminescent element46 would place photoconductive element 16 in a low impedance state, thusallowing potential source 25 to establish a voltage across both sides ofthe electroluminescent crosspoint 32 causing luminescence in thatcrosspoint. Crosspoint 33 would no longer luminesce at the formerbrightness since photoconductive element 18 is in a high impedancestate, thus removing the activating voltage established on that elementby potential source 25.

It is obvious then that by the selective operation of switches 44 and44, any particular series of electroluminescent elements in the matrixmay be activated. Therefore, desired information is fed into the columnand row access units, which information is characterized by theoperation or nonoperation of access switches 44 and 44; and theelectroluminescent matrix 10, in response to '6 the selective switchoperation, may have various portions glowing successively so as to traceout any desired visual pattern.

FIGS. 2A and 2B show the constructional details of one section of therow coordinate access unit, illustrating, respectively, the details ofthe upper and lower sides of the access unit section. Certain of theelements of FIGS. 2A and 2B are counterparts of elements in the circuitof FIG. 1; where there is a correspondence, the elements are similarlydesignated.

Referring to FIG. 2A, the upper surface of a glass plate is coated withtransparent electrically conductive layers 91 and 92. Electroluminescentphosphor layers 142 and 146 and an electrically conductive electrode 93are shown in an exploded view over transparent conductive layers 91 and92. The electroluminescent layers 142 and 144 have their dimensionsalong the XX axis chosen slightly larger than transparent conductivelayers 91 and Q2, while the outer conductive electrode 93 has itsdimensions along the XX axis chosen slightly smaller than theelectroluminescent layers 14-2 and 146, so as to prevent any shortingout between the conductive electrodes when the elements are placedtogether as they would be in normal usage.

FIG. 2B shows the exploded elements of FIG. 2A compressed in theirnormal position and the entire surface rotated 180 degrees toward theviewer about the axis XX, as shown, so that the elements in the lowerside of glass plate of FIG. 2A are now in exploded view. It is apparentthen that the transparent conductive layers 91 and 92 are plated aroundthe edge of the glass plate 90 into the double-square shaped areasshown. The other elements 95, 96, shown in the plane defined bytransparent conductive layers 91 and 2, are also transparent conductivelayers. The dashed lines emanating from these transparent conductivelayers illustrate the areas which the joined photoconductive elementswould be disposed upon in the normal compressed section. For instance,conductive electrode 97 is shown joined with photoconductive element 141and 145, which elements would be attached as shown by the dotted linesonto transparent conductive layers 91 and 92. In a similar manner,conductive electrode 98 is attached to photoconductive element 143, andconductive electrode 99 is attached to photoconductive elements 113 and115, and would also be attached in the position illustrated by thedashed lines.

The layers might advantageously be composed of materials known in theart. For example, the transparent conductive layers 91, 92, 95, and 9 6may be formed of tin oxide; the electroluminescent layers 14 2 and caneither be formed from dielectric suspension of electroluminescentphosphor or from several well-known crystalline films. The conductiveelectrodes might advantageously be formed from some well-known materialsuch as a silver coating.

The arrangement and operation of the above-described section of thecoordinate access unit may be more clearly understood with reference toFIG. 3 which shows the elements illustrated in the exploded view of FIG.2B in their normal position with the exception that conductiveelectrodes 97, 98, and 99, for purposes of illustrative clarification,are now shown as electrical conductors. In addition, crosspoints 28 and31 of the electroluminescent matrix are shown defined by a portion ofelectroluminescent layer 101 sandwiched between the extended transparentconductive electrodes 95 and 9-6 and a second conductive electrode 26which is connected to column coordinate access unit 49 only partiallyshown. The remaining elements correspond to the elements shown in FIGS.2A and 2B and are similarly numbered.

FIG. 3 shows electroluminescent layer 142 sandwiched between conductiveelectrode 93 and transparent conductive layer 91. Conductive electrode93 is connected to potential source 52 by lead 53 attached to lead 51,thereby applying a voltage to one side of electroluminescent layer acress's 142. Photoconductive element 143 is connected in parallel withelectroluminescent layer 142 through conductive layer 93 and lead 53which connects with lead 511. The other side of potential source 52,including potential source 48 and parallel switch 44, is connected bylead t) to conductive electrode 97 which, in turn, establishesphotoconductive element 141 in a series circuit via conductive layer 91with the parallel branch formed by photoconductive element 143 andelectroluminescent layer 142. In the absence of radiation from externalsource 56, as described hereinbefore, the photoconductive elements Mland 143 will be in a high impedance state, thus isolatingelectroluminescent layer 142 from potential source 52.

When it is desired to initiate the operation, light from external source55 is directed to a portion of photocon- 'ductive element 141 via lightchannel 57, which radia tion reduces the impedance of photoconductiveelement 141 slightly. This establishes a conductive path from electrode97 through photoconductive element 14-1 to transparent conductive layer91. With switch 44 in the closed condition, potential source 52 appliesa voltage to the upper portion of electroluminescent layer 142 via theabove-named path; namely, closed switch 44, lead 5d, electrode 97, thereduced impedance of photoconductive element 14-1, and transparentconductive layer l. With one side of potential source 5. connected tothe upper portion of electroluminescent layer 142 and the other side ofpotential source 52 connected to the lower layer of element 142 vialeads 51, 53, and conductive electrode 93, the electroluminescentelement 142 will luminesce dimly. The radiation given oil by the dimlyglowing electroluminescent layer 142 is transmitted through transparentlayer 91 and glass plate 9%? so as to shine fully on photoconductiveelements 113 and 14-1, and shine on a portion of photoconductive element145. This small amount of light, however, is insuflicient to fullyreduce the impedance of any of those elements, and no further operationwould take place at this time without a higher impressed voltageestablished across electroluminescent element 14:2.

The higher potential is developed at a desired instant by the momentaryopening of switch 44 which connects potential source 48 in series withpotential source 52, thereby increasing the potential acrosselectroluminescent element 142 by an amount suificient to cause thatcell to glow brightly. As mentioned earlier, photoconductive element 141and electroluminescent element 1 22 are in a regenerative feedbackrelation sufficient to maintain the series combination so defined in astable on condition after the switch 44 is closed and potential source48 is shunted out.

The operation as thus described with electroluminescent element 142glowing brightly is sufficient to reduce the normally high impedance ofphotoconductive element 113 to a low state. The potential source 25 willtherefore apply a voltage by way of lead 21, conductor 99, low impedanceelement 113, transparent conductive layer 96, and conductive layer 103to one side of the electroluminescent layer 101.

As described earlier, it is necessary to apply voltages of the properintensity to both sides of electroluminescent layer 101 to cause it toluminesce. The procedure thus far described has provided only theapplication of 2. voltage to the bottom side of electroluminescent layer1G1. In a manner similar to that described above, the column access unit4%, also mounted on glass plate 96, would function to reduce theimpedance state of a second input photoconductive element and therebyconnect potential source 25 to conductive electrode 26. It is apparentthen that with potential source 25 connected across the upper and lowersides of electroluminescent layer 161, crosspoint 28, defined by the twoconductive layers 26 and 103, would be activated into luminescence.

The role played by the section shown in FIG. 3 with regard to thecomplete operation of the matrix-access unit combination may moreclearly be understood by stage section of a row coordinate access unit,a portion of a column access unit, and three crosspoints of theelectroluminescent matrix all mounted on a single transparent glassplate 9%). The conductive electrodes 97, 98, 99, and

522. through 105, as mentioned earlier, may advantageously be layers ofnontransparent metal plated on one side of the matrix-access unitcombination.

The other side of the row access unit, shown as dashed lines on FIG. 6,is illustrated in detail in FIG. 4. FIG. 5 illustrates an end view ofthe various layers that comprise the row coordinate access unit in FIGS.4 and 6. Corner portions of the sections shown in FIGS. 4, 5, and 6 havebeen cut away so as to fully illustrate the elements involved in aconstructional layout.

Referring to FIG. 6, the operation would he in accordance with thatdiscussed above wherein the concurrence of light shining from an outsidesource on a portion of photoconductive element 14-1 and the momentaryopening of switch 44 would reduce the impedance of element 141sulficiently to allow the activation of electroluminescent element 142.The brightly glowing electroluminescent element 1 22 is so positioned asto deliver radiation over the full area of photoconductive element 113,which radiation reduces the impedance of that element to allow potentialsource 25 to deliver a voltage to one side of matrix crosspoint 2-8.Assuming throughout the rest of the discussion that electroluminescentelement 50', partially illustrated by dashed lines in column access unit49, is also glowing brightly, then photoconductive element 114 wouldalso be in a low impedance state allowing potential source 25 to deliveran activating voltage to matrix crosspoint 28, via conductive layer 26.

The dashed outline of electroluminescent element 142 illustrates thatphotoconductive element is positioned to receive a portion of theradiation delivered by element 142. This small amount of radiationreceived by element 14d lowers that elements impedance allowingpotential source 52 to apply suificient voltage acrosselectroluminescent element 145 to cause that element to glow dimly. Asubsequent momentary opening of switch 44 delivers a voltage sufficientin magnitude to fully activate electroluminescent element 4-6. Thebrightly glowing electroluminescent element 146 directs radiation tophotoconductive element 143 lowering the impedance of that element whichis connected in parallel with electroluminescent element 142 bytransparent conductive layer 91 and conductive electrodes 93 and 98.This condition causes a reduction in the voltage acrosselectroluminescent element 142 to such a low point that element 242 isextinguished.

This operation assures that element 146 is in an activated condition andelement 142 is in an unactivated condition which, in turn, means thatphotoconductive element 115 is in a low impedance condition whilephotooonductive element 113 reverts to its high impedance state. Thus,potential source 25 is removed from electroluminescent matrix crosspoint28 and is connected through the low impedance of element 115 to one sideof crosspoint 31. Since the column access unit is holdingphotoconductive element 114 in a low impedance state, potential source2-5 will thereby activate cross point 31.

The procedure just described will again take place with the momentaryopening of switch 44 to bring the third stage of electroluminescentelement into activation and extinguish the second stage ofelectroluminescent element 146. Photoconductive element 115 will therebyrevert to its high impedance state, removing potential source 25 frommatrix crosspoint 31 and, in turn, applying potential from source 25through the low impedance of photoconductive element 117 to matrixcrosspoint 34. This procedure then causes matrix crosspoint 34 to glowbrightly.

The operation as described above might advantageously have the radiationfrom the last electroluminescent element fed back to the firstphotoconductive element to maintain the access unit in a continued stateof activation, and according to a preselected operation of the switches44 and 44', trace out any desired pattern on the matrix screen by theselected activations of particular matrix crosspoints.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of this invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of this invention.

What is claimed is:

1. In combination, an electroluminescent matrix having a plurality ofcrosspoints defined by row and column conductors contiguously positionedon opposite sides of a layer of electroluminescent material, a pluralityof light-responsive switch means spaced in said matrix apart from saidcrosspoints and having a pair of said plurality of switch meansassociated with each of said crosspoints, access circuit meanspositioned in a light transfer relation With said light-responsiveswitch means and including a plurality of electroluminescent elementshaving distinct elements of said plurality optically aligned with saidlightresponsive switch means and activating means being operable toestablish luminescence in a selected pair of said plurality ofelectroluminescent elements, and means including a pair of saidlight-responsive switch means responsive to the luminescence in saidselected pair of electroluminescent elements for activating thecrosspoint common to said pair of light-responsive switch means.

2. In combination, an electroluminescent matrix having a plurality ofcrosspoints defined by row and column conductors positioned on oppositesides of a layer of electroluminescent material, said crosspoints beingmaintained in a normally unactivated condition by lightresponsive switchmeans connected thereto, and access circuit means positioned in a lighttransfer relationship for operating said light-responsive switch meansin said matrix, said access circuit means including a plurality ofelectroluminescent elements and activating means being operable toestablish luminescence in consecutive ones of said electroluminescentelements, said activating means comprising a plurality oflight-responsive means, means connecting each or" said light-responsivemeans in a series circuit with one of said plurality ofelectroluminescent elements, a voltage source, and means connecting saidseries circuits in parallel with said source to establish voltage fromsaid source across said electroluminescent elements upon the externalexcitation of a distinct one of said light-responsive switch meanswhereby one of said plurality of electroluminescent elements glowsbrightly.

3. The combination in accordance with claim 2 and further comprisingmeans for shunting one of said plurality of voltage sources to cause oneof said plurality of electroluminescent elements to glow dimly.

4. In combination, a matrix comprising a plurality of row and columnconductors positioned on opposite sides of a layer of electroluminescentmaterial, potential means for energizing a selected portion of saidelectroluminescent layer, light-responsive means normally in a highimpedance condition connected between said potential means and saidconductors, and access circuit means positioned in a light transferrelation with said light-responsive switch means including a pluralityof electroluminescent elements and activating means for establishingluminescence in consecutive ones of said electroluminescent elements,each of said luminescent elements reducing the high impedance state inassociated ones of said light-responsive means.

5. The combination in accordance with claim 4 wherein saidlight-responsive switch means comprises photoconductive elements.

6. The combination in accordance with claim 4 wherein said activatingmeans comprises a first potential source connected in parallel with saidplurality of electrolumines- 10 cent elements, and a second potentialsource intermittently connected in series with said first potentialsource to activate selected ones of said plurality of electroluminescentelements.

7. In combination, a matrix comprising a plurality of row and columnconductors positioned on opposite sides of a layer of electroluminescentmaterial, a first potential source, a plurality of normally highimpedance lightresponsive means connected between said first potentialsource and said conductors to hold said matrix in an unactivatedcondition, and access circuit means for reducing the normally highimpedance of selected Ones of said plurality of light-responsive meansto allow cur-rent flow from said source through said layer, said accesscircuit means including a plurality of normally unactivatedelectroluminescent elements positioned in light transfer relationshipwith corresponding ones of said light-responsive means and potentialmeans to cause consecutive ones of said normally unactivatedelectroluminescent elements to luminesce.

8. An electro-optical circuit combination comprising anelectroluminescent matrix having first photo-conductive and firstelectroluminescent elements electrically connected with each other, andan access circuit comprising second photoconductive elements and secondelectroluminescent elements electrically connected with each other in aplurality of series circuits, a potential source,

. and means for applying a voltage from said source in parallel to saidplurality of series circuits, external means for activating a distinctone of said photoconductive elements to establish sufficient voltagefrom said source across one of said electroluminescent elements forcausing said element to glow dimly, a second potential sourceintermittently connected in series with said first potential source toestablish sufficient voltage across said dimly glowing element forcausing said element to glow brightly, each of said secondelectroluminescent elements connected in optical relationship with oneof said first photoconductive elements to transfer light thereto, andmeans including a third plurality of photoconductive elements connectedin parallel circuits in light transfer relationship with said secondelectroluminescent elements to consecutively activate said plurality ofsecond electroluminescent elements.

9. An electro-optical circuit combination comprising anelectroluminescent matrix defined by a plurality of column and rowconductors positioned on opposite sides of a layer of electroluminescentmaterial, first source means for applying a voltage to said conductors,first variable impedance elements electrically connected between saidsource and said conductors, a plurality of light generating elementseach optically connected to one of said first variable impedanceelements, a plurality of second and third variable impedance elements,means connecting each of said light generating elements in parallel withone of said second variable impedance elements in a plurality ofparallel circuits, means connecting each of said third variableimpedance means in series with one of said parallel circuits and in aplurality of series circuits, second source means for applying a voltageacross said series circuits to activate one of said light generatingelements upon external excitation of one of said second plurality ofvariable impedance means, and third source means for intermittentlyapplying a voltage to said series circuit to increase the activation ofsaid light generating element.

10. In combination, a matrix comprising a plurality of transparent rowand column conductors positioned on opposite sides of a layer ofelectroluminescent material, means for energizing a selected portion ofsaid electroluminescent layer comprising a first potential source, firstlight-responsive means connected between said first potential source andsaid conductors and means for selectively activating saidlight-responsive means to permit current conduction from said sourcethrough said layer,

said activating means comprising a plurality of electroluminescentelements positioned to illuminate corresponding portions of saidlight-responsive means, and means for selectively energizing saidelectroluminescent elements comprising a second potential source, secondlight-responsive means connected between said second potential sourceand corresponding ones of said electroluminescent elements, and a lightsource for activating a distinct one of said second light-responsivemeans to permit current conduction from said second potential sourcethrough one of said electroluminescent elements.

ll. The combination in accordance with claim further comprising a thirdpotential source and means for selectively connecting said thirdpotential source between said second light-responsive means and saidsecond potential source.

12. The combination in accordance with claim 11 wherein said connectingmeans includes a switch means connected in parallel with said thirdpotential source.

13. In combination, an electroluminescent matrix including firstphotoconductive elements and first electroluminescent elementselectrically connected with each other and an access circuit for saidmatrix comprising a plurality of second and a plurality of thirdphotoconduc tive elements, a plurality of second electroluminescentelements, means connecting each of said second photoconductive elementsin parallel with one of said second electroluminescent elements in .aplurality of parallel circuits, means connecting each of said thirdphotoconductive elements in series with one of said parallel circuitsand in a plurality of series circuits, first source means for applying avoltage to said series circuits to cause a second electroluminescentelement to glow dimly on external excitation of the thirdphotoconductive element connected in series therewith, and second sourcemeans for intermittently applying a voltage to said series circuits forcausing sufiicient current to flow through said dimly glowingelectroluminescent element to cause said element to glow brightly, eachof said second electroluminescent elements being in light transferrelationship with one of said first photoconductive elements in saidmatrix.

14. The combination in accordance with claim 13 wherein each of saidsecond electroluminescent elements is further in light transferrelationship with one of said third photoconductive elements connectedin one of said.

parallel circuits for shunting sufficient current away from one of saidsecond electroluminescent elements to hold that element in anunactivated condition.

15. A matrix-access unit combination comprising a common transparentinsulating support member, a matrix having a plurality of crosspointsdefined by a layer of electroluminescent material contiguously,positioned between a first and second plurality of distinct parallelconductive layers on one surface of said member, potential means forenergizing selected ones of said plurality of crosspoints, and accesscircuit means having a plurality of distinct light-responsive electrodesdisposed on each of said first and second plurality of conductivelayers, said access circuit means further comprising electroluminescentmeans positioned on the other side of said member in a light transferrelation with said lightresponsive electrodes and means for establishingluminescence in consecutive ones of said electroluminescent means toactivate corresponding ones of said lightresponsive electrodes. I

16. An electro-optical circuit combination comprising a transparentinsulating support member, a first plurality of parallel separatedtransparent conductive layers disposed in a first direction on one sideof said support memher, a second plurality of parallel conductive layersextending along another direction of said support member, a layer ofelectroluminescent material contiguous with said first and secondplurality of conductive layers positioned to leave a portion of each ofsaid first and second plurality of conductive layers exposed, apotential source, distinct light-responsive electrodes connected to saidpotential source and disposed on each of said exposedeportions of saidfirst and second plurality of conductive layers, and means forselectively activating said lightresponsive electrode means comprising aplurality of electroluminescent elements positioned on the other side ofsaid insulating support member in light transfer relation with saidlight-responsive electrodes.

17. An electro-optical circuit combination in accordance with claim 16wherein said means for selectively activating said light-responsiveelectrodes further comprises a first potential source to establish avoltage sufiicient in magnitude to partially activate the selected oneof said plurality of electroluminescent elements and a second potentialsource selectively connectable in series with said first potentialsource to establish a voltage sufficient to fully activate saidpartially activated electroluminescent element.

18. in combination, an electroluminescent matrix including a firstplurality of photoconductive elements and first electroluminescentelements in optical relationship with each other, means for energizingselected ones of said plurality of photoconductive elements comprising aplurality of second and a plurality of third photoconductive elements, aplurality of second electroluminescent elements, means connecting eachof said second photoconductive elements in parallel with one of saidsecond electroluminescent elements in a plurality of parallel circuits,means connecting each of said third photoconductive elements in serieswith one of said parallel circuits in a plurality of series circuits,first source means for applying a voltage to said series circuit tocause a second electroluminescent element to glow dimly on externalexcitation of a distinct photoconductive element connected in seriestherewith, and second source means for intermittently applying a voltageto said series circuits for causing sufficient current to flow throughsaid dimly glowing electroluminescent element to cause said element toglow brightly, each of said second electroluminescent elements being inlight transfer relationship with one of said first photoconductiveelements in said matrix and one of said third photoconductive elementsin said parallel circuits, said third photoconductive element operativefor shunting sufiicient current away from said brightly glowing elementto extinguish said element.

19. In combination, a matrix comprising a transparent insulating supportmember, a first plurality of parallel separated transparent conductivelayers disposed in a first direction on one side of said support member,a second plurality of parallel conductive layers extending along anotherdirection of said support member, a layer of electroluminescent materialcontiguous with said first and second plurality of conductive layerspositioned to leave a portion of each of said first and second pluralityof conductive layers exposed, a first source, a first plurality ofphotoconductive elements disposed on each of said exposed portions ofsaid first and second plurality of conductive layers, means connectingsaid photoconductive elements to said first source to maintain saidelectroluminescent layer in an unactivated condition, and access circuitmeans comprising a first plurality of electroluminescent elements, asecond and third plurality of photoconductive elements disposed onconductive coating means connecting each of said second plurality ofphotoconductive elements in parallel with one of said firstelectroluminescent elements in a plurality of parallel circuits, saidconductive coating means further connecting said third plurality ofphotoconductive elements in series with one of said parallel circuitsand in a plurality of series circuits, a second source, conductive layermeans connecting said second source to said series circuits for applyinga voltage to said series circuits to cause a first electroluminescentelement to glow dimly on external excitation of the thirdphotoconductive element connected 13 in series therewith, a third sourcefor intermittently applying a voltage to said series circuits forcausing sufiicient current to flow through said dimly glowingelectroluminescent element to cause said element to glow brightly, eachof said first electroluminescent elements positioned in light transferrelationship on the opposite References Cited in the file of this patentUNITED STATES PATENTS Jay Apr. 12, 1960

1. IN COMBINATION, AN ELECTROLUMINESCENT MATRIX HAVING A PLURALITY OFCROSSPOINTS DEFINED BY ROW AND COLUMN CONDUCTORS CONTIGUOUSLY POSITIONEDON OPPOSITE SIDES OF A LAYER OF ELECTROLUMINESCENT MATERIAL, A PLURALITYOF LIGHT-RESPONSIVE SWITCH MEANS SPACED IN SAID MATRIX APART FROM SAIDCROSSPOINTS AND HAVING A PAIR OF SAID PLURALITY OF SWITCH MEANSASSOCIATED WITH EACH OF SAID CROSSPOINTS, ACCESS CIRCUIT MEANSPOSITIONED IN A LIGHT TRANSFER RELATION WITH SAID LIGHT-RESPONSIVESWITCH MEANS AND INCLUDING A PLURALITY OF ELECTROLUMINESCENT ELEMENTSHAVING DISTINCT ELEMENTS OF SAID PLURALITY OPTICALLY ALIGNED WITH SAIDLIGHTRESPONSIVE SWITCH MEANS AND ACTIVATING MEANS BEING OPERABLE TOESTABLISH LUMINESCENCE IN A SELECTED PAIR OF SAID PLURALITY OFELECTROLUMINESCENT ELEMENTS, AND MEANS INCLUDING A PAIR OF SAIDLIGHT-RESPONSIVE SWITCH MEANS RESPONSIVE TO THE LUMINESCENCE IN SAIDSELECTED PAIR OF ELECTROLUMINESCENT ELEMENTS FOR ACTIVATING THECROSSPOINT COMMON TO SAID PAIR OF LIGHT-RESPONSIVE SWITCH MEANS.